MINOR: config: Parse the string of the log-format config keyword

parse_logformat_string: parse the string, detect the type: text,
        separator or variable

parse_logformat_var: dectect variable name

parse_logformat_var_args: parse arguments and flags

add_to_logformat_list: add to the logformat linked list
diff --git a/include/types/proxy.h b/include/types/proxy.h
index d0bc51c..6693d82 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -286,6 +286,7 @@
 	int (*accept)(struct session *s);       /* application layer's accept() */
 	struct proxy *next;
 	struct list logsrvs;
+	struct list logformat; 			/* log_format linked list */
 	int to_log;				/* things to be logged (LW_*) */
 	int stop_time;                          /* date to stop listening, when stopping != 0 (int ticks) */
 	struct hdr_exp *req_exp;		/* regular expressions for request headers */